Ultrastructure of cytoskeletal elements of endothelial and stromal cells of rat marrow.

This study reports the distribution of microfilaments, microtubules, and intermediate filaments in endothelial cells, reticular cells, and macrophages of bone marrow of rats following fixation with glutaraldehyde, tannic acid, and saponin. In endothelial cells bundles of microfilaments are seen along the basal surface, where these cells adhere to underlying extracellular materials. The reticular cells, especially those that are closely associated with the endothelium of sinusoids, contain many intermediate filaments and microtubules as well as microfilaments. The reticular cell processes that partially cover the endothelium and extend among the blood cells have numerous microtubules and intermediate filaments arranged longitudinally within them; these cytoskeletal elements appear to provide mechanical support for the processes. Macrophages also have many microtubules and intermediate filaments but these organelles do not extend into the thin processes of these cells as is the case with reticular cells. Bundles of microfilaments are observed in the cytoplasm of adventitial and endothelial cells at sites where migrating blood cells are attached to these cells producing local regions of stress.